When the 34th America’s Cup begins on Saturday it will do so in a
flood tide. In fact, the first eight races are likely to be held in a
flood tide (flowing into San Francisco Bay), which will then turn to an
ebb tide (flowing out of the Bay) beginning on the second weekend.

“Two years ago we started looking at the currents for the race days
of the America’s Cup and how that affects the tactics,” said ORACLE TEAM
USA tactician John Kostecki. “Basically, the current affects the
windspeed and it’ll play a major factor.”

A flood tide is favorable because it means the current is moving the
same direction as the prevailing west/west-southwesterly wind and
increases the wind limit for racing, which in the America’s Cup is set
at a base of 23 knots. The limit will increase or decrease daily based
on the strength and direction of the tide. A flood tide means less chop
and flatter water, while the ebb churns up the water, as the wind is
against the current.

In the Louis Vuitton Cup the crews sought relief from the flood tide
in the lee of Alcatraz Island on the bottom of the windward leg.

“It is quite interesting having Alcatraz as part of the race track,”
said Kostecki, who says he has sailed on the Bay for more than 45 years.
“It really comes into play because on flood tides you can use the cone
of Alcatraz as relief. You can get about 3 to 4 knots difference in tide
just from behind the island.

“The speed of the tide on the racecourse can vary a fair amount,”
Kostecki continued. “I have seen up to 4.5 to 5 knots in strength in the
middle of the Golden Gate Bridge. On the race track it will be a little
bit less, but you could see 3 to 3.5 knots on the racecourse in a
really strong tide, and that really makes it interesting for us
tacticians as to where we place the boat to take advantage of the
strength of the tide.”

The strength of the tide is particularly important downwind,
especially with the advent of hydrofoiling. Normally, a tactician would
look for slack water sailing downwind in an adverse current. But with
the AC72’s ability to hydrofoil, tacticians are now looking for more
adverse current.

“It’s completely contrary to everything they’ve done in their sailing
careers,” said ACTV commentator Ken Read, a veteran of two Volvo Ocean
Races and countless grand-prix regattas. “Adverse current is helping
downwind because the conveyer belt is moving against the wind and
increasing the apparent windspeed the boat feels. Windspeed is king in
the AC72. Increasing the windspeed makes up for the adverse current.”

If one of the crews wants to hydrofoil upwind they’ll be looking to
avoid adverse current because it slows the apparent windspeed. The
jury’s still out as to the benefits up upwind hydrofoiling, but Emirates
Team New Zealand tactician Ray Davies thinks it will occur.

“It’s almost routine now,” said Davies. “I’d expect it to play a role in the Cup.”